This section provides background information related to the present disclosure which is not necessarily prior art. This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
Diluting Spark-Ignited (SI) stoichiometric combustion engines with excess residual gas reduces throttling losses and improves thermal efficiency. In normal operation, the spark is advanced towards Maximum Break Torque (MBT) timing. However, combustion instability, misfire, and knock limit the feasible range of spark timings. For certain operating conditions, it is desirable to continuously operate at the border of the feasible spark region. For instance, with high Exhaust Gas Recirculation (EGR) dilution, the MBT timings are located at a spark advance beyond the misfire limits.
Traditionally, spark timing is an open-loop feed forward control with misfire limits determined for a specific engine from extensive experiments covering a large range of speed, torque, and actuator settings. To extend the benefits of dilute combustion while at the misfire limit, it is essential to define a parameterizable, physics-based model capable of predicting the misfire limit as operating conditions change based on driver demand.
According to the principles of the present teachings, a predictive modeling and mitigation methodology is provided to predict and mitigate misfire occurrence and combustion phasing in a variable volume SI engine system. The misfire model describes the early flame development period of 0 to 3 percent mass fraction burned and considers the effect of ignition characteristics, local fuel to air equivalence ratio, flame kernel initiation, and planar flame interaction with in-cylinder turbulence.
In some embodiments, the present teachings provide a method and apparatus to predict and enable control of misfire that influences combustion cyclic variation and COV of IMEP in spark-ignited (SI) engine. The method can include obtaining engine data and determining temperature and pressure within a cylinder in response to engine data; determining crank angle resolved flame velocity evolution based on the engine data; comparing the crank angle resolved flame velocity to predetermined turbulent combustion regime data to determine a misfire occurrence; and updating a misfire occurrence indicator and outputting a control signal when the misfire occurrence indicator is greater than a predetermined limit, the control signal being capable of adjusting any engine actuator, such as external ignition source on a cycle to cycle basis of the spark-ignited engine. The method and apparatus can further include correlating the crank angle resolved flame velocity to combustion phasing when the misfire occurrence indicator is less than the predetermined limit.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
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